Virulence and diversity of Puccinia striiformis f. sp tritici in Ethiopia

Stripe rust of wheat (Triticum spp.), caused by Puccinia striiformis f. sp. tritici, is an important disease in Ethiopia. To investigate the population structure of the pathogen, 107 single-pustule isolates were collected from four regions (northern, central, southern, and southeastern Ethiopia) and tested on 24 differential genotypes with known resistance genes. The isolates were classified into 39 pathotypes. All isolates were virulent on Yr7 and avirulent on Yr1, Yr5, Yr15, and YrSp. Virulence complexity of the isolates ranged from 7 to 16, with a mean of 11.72. No common pathotype was shared by these regional collections. Distribution of pathotypes within the regions was quite even, whereas the richness of populations varied considerably between 1.78 (the central region) and 2.96 (the southeastern region). The genotypic, gene, and genetic diversities within populations were characterized using the Simpson, Nei, and Kosman indices. Significant differences among the regional populations were detected for both gene and genetic diversity within populations, whereas the genotypic diversity was rather stable. The lowest and highest diversities of wheat stripe rust occurred in the southern and northern regions, respectively. Genetic variation in the population structure of the pathogen observed in different geographical areas might indicate that unique wheat cultivars should be developed and released for production on a regional basis.